Control system for individually driven vehicles in a train of such vehicles

ABSTRACT

Control system for trains of the type in which each car in the train is powered by its own drive motor means (e.g., a commuter train). Cars are addressed individually by train lines including an advance control train line which facilitates picking up an advance relay in each car successively by increasing the voltage on the advance train line in steps. The system minimizes the number of required train lines while insuring smooth acceleration and deceleration of the train.

United States Patent 1 Eisele et al.

[451 July 17,1973

CONTROL SYSTEM FOR INDIVIDUALLY DRIVEN VEHICLES IN A TRAIN OF SUCHVEHICLES Inventors: Hermann Eisele, Nellingen, Germany; Robert R. Lewis,Pittsburgh, Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: July 29, 1971 Appl. No.: 167,140

Assignee:

References Cited UNITED STATES PATENTS 11/1971 Franke et a1 105/61 XTRAIN LINES 3,601,671 8/1971 Little 318/102 Primary Examiner--Gerald M.Forlenza Assistant Examiner-GeorgeI-1. Libman Attorney-F. H. Henson, R.G. Brodahl and Jack M. Arnold [S 7] ABSTRACT Control system for trainsof the type in which'each car in the train is powered by its own drivemotor means (e.g., a commuter train). Cars are addressed individually bytrain lines including an advance control train line which facilitatespicking up an advance relay in each car successively by increasing thevoltage on the advance train line in steps. The system minimizes thenumber of required train lines while insuring smooth acceleration anddeceleration of the train.

11 Claims, 5 Drawing Figures CONTROL SYSTEM FOR INDIVIDUALLY DRIVENVEHICLES IN A TRAIN OF SUCH VEHICLES BACKGROUND OF THE INVENTION In aconventional subway system or the like, all the cars in the train arecontrolled simultaneously by train lines. As soon as a train line isenergized or deenergized, a relay is picked up or dropped in every carwhile the whole train moves to a higher or lower power position. With acontrol system of this type, the torque in the motoring mode can only bechanged in coarse steps for positions which allow continuous operation.This ordinarily results in rough operation (e.g., jerks) duringacceleration or deceleration. This is due, at least in part, to thenormal play in the couplers between cars.

The operation of a train of this type can be improved with a controlsystem wherein the head-end can address each car individually insequence. That is, a smoother ride can be effected by addressing carsindividually with a so-called advance control train line which allowspicking up advance relays successively in each car by increasing thevoltage on an advance train line in steps. In this way, one car afteranother will move successively to the next higher power position; thesmoothness of the ride will be improved; and the cars can only be apartby one step from any other car in the train.

In any advance control train line system of this type, it is naturallydesirable to use as few individual train lines as possible. An advancecontrol train line system can be effected utilizing only two or threetrain lines, when three train lines are used one is an advance trainline and the other two of which have steady-state voltages selectivelyapplied thereto. The problem with systems utilizing only two or threeindividual train lines, however, is that they require perfect timing ofthe voltage signals applied to the main train lines and the advancecontrol train line, combined with a guaranteed fast response of theadvance train line relays and slow response of the main relays. In anactual application with many subway cars, for example, this representsan impractical solution because of the tight tolerances required.

SUMMARY OF THE INVENTION In accordance with the present invention, acontrol system is provided for addressing powered cars in a trainindividually in an advance control train line arrangement wherein thetrain lines need only be energized in a given sequence, without regardto accurate timing. This requires the addition of a another train linewhich, while increasing the complexity of the system slightly, enablesthe cars of the train to be addressed in sequence without precisetiming.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part'of this specification,and in which:

FIG. 1 is a schematic circuit diagram of a type of circuit forsequentially energizing electrical relays, usable in the circuitry ofthe invention;

.FIG. 2A is a schematic circuit diagram of one embodiment of theinvention for addressing cars in a train sequentially;

FIG. 2B is a timing diagram showing the sequence of operation of therelays of FIG. 2A;

FIG. 3A is a schematic circuit diagram of another embodiment of theinvention; and

FIG. 38 illustrates the timing sequence of the relays for the embodimentof the invention shown in FIG. 3A.

With reference now to the drawings, and particularly to FIG. 1, thecircuit shown is adapted to energize relays in sequence as a source ofvoltage applied to a train line is increased. This circuitry is utilizedin the present invention and is the subject of copending applicationentitled Apparatus For Sequentially Electrical Utilization Devices, Ser.No. 167,139, filed July 29, 1971, on behalf of Thomas C. Matty andRobert H. Perry and assigned to the Assignee of the present application.A train control circuit or controller 10 is connected between a trainline A and a common bus 12 as shown. The train control circuit 10 isadapted to produce an output between line A and bus 12 which increasesin steps, as hereinafter described in detail. Included in series intrain line A are two diode bridge circuits 14 and 16 each comprised offour diodes D1, D2, D3 and D4 placed around a relay R or R,,. The relaysR and R, are connected in series with transistors 18 and 20 between theupper terminal 22 of each bridge 14 or 16 and the bus 12. The upperterminal 22 of the bridge 14 is connected through a voltage dividerarrangement comprising Zener diode Z1 and resistor 24 to the power bus12, the junction of Zener diode Z1 and resistor 24 being connected tothe base of transistor 18. In a similar manner, terminal 22 of bridge 16is connected through Zener diode Z2 and a resistor 26 to the power bus12, the junction of Zener diode Z2 and resistor 26 being connected tothe base of transistor 20.

Because of the diodebridge circuits 14 and 16, the circuit of FIG. 1will operate to energize the relays R and R, in response to a voltageapplied to either end of a string of such relays connected betweenconductors A and 12. It is necessary only that the train line A bepositive with respect to bus 12 so as to reverse bias the Zener diodesZ1, Z2, and so on.

With no voltage applied across conductors A and 12 from the traincontrol circuit 10, both relays R, and R, will be deenergized. However,if a step voltage from train control circuit 10 is applied acrossconductors A and 12, relay R, will be initially energized through diodeD1 and transistor 18 until the point is reached where Zener diode Z1breaks down, thereby cutting off the PNP transistor 18 because of therise in voltage at its base. The current through relay R, is nowdiverted through diode D3 of bridge 14 and the diodeDl' in bridge 16 torelay R, and transistor 20, which is now conducting. This will continueuntil the voltage from train control circuit 10 reaches the point whereZener diode Z2 breaks down and cuts off PNP transistor 20; whereupon thecurrent through relay R', will now be diverted through the next relay,and so on, until the entire string of relays is energized in sequence.Thus, increases in the voltage across conductors A and 12 causesuccessive relay energizations with an approximate constant current loadon the line. As will be seen hereinafter, the relays R R, and so on, arecarried on successive cars in a train of cars such that the torqueexerted by the cars will be increased or decreased one after the otheras the voltage from train control circuit 10 is increased in steps.

With reference now to FIG. 2A, a complete train control system is shownwhich again includes the train control circuit 10 having four trainlines 1, 2, A and D.

Relays RA for car Nos. 1 and 2 in FIG. 2A correspond to and perform thesame function as relays R and R respectively in FIG. 1. That is,successive ones of the relays in the Zener diode sequential firingcircuitry of FIG. 1 are carried on successive cars on the train therelay R in car ii and car 2 respectively is shown connected directly tothe lower bus bar for ease of illustration only. Also carried on eachcar are additional relays RD, R3, R2, and R1. Relay R1 is connectedbetween train line 1 and common bus 12 and is energized when train line1 is energized. The relay R2 is connected between train line 2 andcommon bus 112 through diode 32 in each car and can be energized throughthat diode when train line 2 is energized or when relays RA and RD areenergized and train line 1 is energized. That is, when relays RA and RDare energized, contacts A-11 and D-il will close, thereby enablingenergization of relay R2 through the aforesaid contacts A-H and D-1 anddiode 34. Relay RD is energized in each car only when train line D isenergized.

Relay R3 can be energized when train line 2 is energized and when relaysRA and RD are energized, thereby closing contacts A-2 and D-2. In thiscase, the relay R3 in any car is energized through contacts A-2 and D-2and diode 36.

The drive motor system for each car is simplified in FIG. 2A forpurposes of explanation. The drive motors for each car in a train areidentified in FIG. 2A as M1, M2, M3 and M4. These can be connected inseries through normally closed contacts 3-4; or, when contacts 3-4 openand contacts 33 and 3-5 close, motors M1 and M2 will be connected inparallel with motors M3 and M4. The armatures of all motors Nil-M4 areconnected in series with resistors 38, dd and $2, with resistors 38 and40 being shunted by normally open contacts 2-3 and 2-4 of relay R2.Power is initially supplied to the motors Ml through M4 when relay R1 isenergized and contacts 1-1 close.

The manner in which the torque produced by the drive motors issuccessively increased or decreased will now be described in connectionwith FIG. 2B. Regardless of whether it is desired to increase ordecrease torque, the train line 1 must be energized, thereby energizingrelay R1. This, then, closes contacts H'-li in each car. Additionally,when it is desired to increase torque and accelerate, the relay RD mustbe energized; however during deceleration when torque is decreasing,relay RD'is deenergized, as is the train line D.

Assuming, for the moment, that it is desired to increase torque, trainline D will be energized as will relay RD, thereby closing contacts D-1and D-2. At time t, in FIG. 28, a step voltage is applied to train lineA, thereby causing the circuit 28, similar to one of the diode bridgecircuits of FIG. I, to energize the relay RA in car 1. When relay RA incar 11 is energized, contacts A] close and relay R2 is energized throughtrain line 1, contacts A-1 and D-1 and diode 34. When relay R2 isenergized, contacts 2-3 and 2-4 are closed, thereby shorting outresistors 38 and 40 in series with the motors Ml-M4 as thecounterelectromotive force of the motor increases. At time I the voltageon train line A is again increased, whereupon relay IRA for car 2 isenergized, and contacts 2-3. and 2-4 for car 2 close; whereupon thetorque produced by the motors for car 2 increases. At time train line Ais deenergized as are relays RA in each car. Then, at time train line 2is energized, but nothing happens at this precise time since relay R3cannot be energized with contacts A-2 open. At time i relay RA in car 1again becomes energized, whereupon relay R3 becomes energized sincecontacts A-2 are now closed. When relay R3 becomes energized, contacts3-4 open and contacts 3-3 and 3-5 close, thereby connecting the motorsM1-M4 in a series-parallel arrangement whereby the torque of the car isincreased while its speed increases. At time t,,, the voltage on trainline A is increased, whereupon relay IRA for car 2 becomes energized andmotors Ml-M4 for car 2 are connected in a series-parallel arrangementsimilar to the motors for car 1. This progresses down the string of carsfrom one car to another in succession until all of the motors in therespective cars are connected in a series-parallel arrangement.

Now, if it is desired to decrease the torque of the motors at time forexample, the train line D is deenergized. Thereafter, at time t thevoltage on train line A is decreased; whereupon relay RA for car 2becomes deenergized as does relay R3 for car 2 such that the motorsNil-M4 for car 2 are again connected in series. At time train line A isdeenergized, which deenergizes relay RA for car 1, causing relay R3 forcar 1 to drop out and connecting motors M 1-M4 for car 1 in series. Attime r train line A is again energized to a voltage level where relaysRA in both cars l and 2 will be energized; at time t train line 2 isdeenergized; and at time the voltage on train line A is decreased to thepoint where relay RA in car 2 drops out, whereupon relay R2 for car 2drops out also and contacts 2-3 and 2-4 for car 2 again open to insertresistors 38 and 40 in series with the motors M1-M4. At time train lineA is deenergized and the same action takes place for car 1 with relay R2dropping out and resistor 38 and 40 again being inserted in series withthe armatures of motors Mil-M4 for car 1.

In FIGS. 3A and 38, an arrangement similar to that of FIGS. 2A and 2B isshown, except that instead of providing a directional train line, a holdtrain line H is provided. In this case, relay R1 is energized from trainline I as in the embodiment of FIG. 2A. Relay R2 in any car can beenergized through diode 43 from train line 2 or through diode and holdline H when contacts 2-11 of relay R2 are energized. Finally, relay R2can be energized from train line 1, assuming that contacts A-l of relayRA are closed. Relay R3 can be energized from hold line H through diode46 and contacts 3-1 of relay R3 or from train line 2 through contactsA-2 if relay RA is energized. The relays RA in each car are againenergized from train line A through circuits 48 and 50 whichcompriseZener diode delay circuits similar to those shown in FIG. 1. Themotor circuits for the respective cars are not shown in FIG. 3A; howeverit will be appreciated that the relays R1, R2 and R3 perform the samefunctions as they did in the embodiment of FIG. 2A.

The operation of the embodiment of the invention shown in FIG. 3A canbest be understood by reference to FIG. 3B. Regardless of whether thetractive efi'ort is being increased or decreased, train line 1 isenergized, as are relays R1 in each car 1 and 2. At time 2,, train lineA is energized to energize relay RA for car 1. When relay RA becomesenergized, contacts A-l close, thereby energizing relay R2. At time 2,,the same action occurs for car 2 in response to an increase in voltageon train line A, thereby energizing relay R2 for car 2. At time t thehold line H is energized; and since contacts 21 of relay R2 are closedat this time, relay R2 remains energized even though the voltage ontrain line A should drop to zero. At time t train line 2 becomesenergized, whereupon relay R2 will remain energized through diode 43. Upto this point, therefore, the relays R2 in cars l and 2 have beenenergized in succession. At time 1 the hold train line H is deenergized;however this has no effect since the relay R2 remains energized throughtrain line 2 which is now energized. At time the train line A is againenergized to energize relay RA; and at time t,, the voltage on trainline A is increased to energize the relay RA in car 2. This has theeffect of energizing relays R3 in cars l and 2 at times and t-,,respectively.

During a deceleration cycle, the process is reversed. At time t,,, thevoltage on train line A is decreased, thereby deenergizing relay RA forcar 2 and deenerging relay R3. At time the voltage on train line A dropsto zero, deenergizing relays RA and R3 in car 1. At time 1 the hold lineH is again energized; and at time the voltage on train line 2 drops tozero; however relay R2 remains energized through the hold line H, diode44 and contacts 2-1 in each car. At time the voltage on train line A isincreased to the point where both relays RA in cars 1 and 2 areenergized; and at time the hold line voltage decreases to zero.Therefore, when the voltage on train line A at time t drops to one-halfits original value, relay RA in car 2 becomes deenergized as does relayR2. At time 1 the voltage on train line A drops to zero, relay RA forcar 1 becomes deenergized, and so also does the relay R2 for car 1because contacts A1 are now open.

It can be seen that the sequence of operations is similar to that forthe embodiment shown in FIGS. 2A and 28, with the exception that a holdvoltage is employed rather than a directional voltage on one of thetrain lines.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

We claim as our invention:

1. In a control system for selectively increasing and decreasing thetorque exerted by each of plurality of vehicle cars operative as avehicle train, each such vehicle car having individual vehicle car drivemeans controlled by a plurality of bistable devices, the combinationcomprising:

control means for providing at least one vehicle control signal; and

means, in a given one of said vehicle cars, including an electronicallycontrolled series conduction path between said given one of said vehiclecars and a second vehicle car with a given one of said plurality ofbistable devices being included in said series conduction path and beingresponsive to said one vehicle control signal being at a firstpredetermined level for changing the state of said given one of saidplurality of bistable devices for increasing the torque exerted by saidone vehicle car, said means being responsive to said one vehicle controlsignal being at a second predetermined level for changing the conditionof said series conduction path from open to closed for transmitting saidone vehicle control signal from said one vehicle car to said secondvehicle car for increasing the torque exerted by said second vehiclecar.

2. In a control system for selectively increasing and decreasing thetorque exerted by each of a plurality of vehicle cars operative as avehicle train, each such vehicle car having individual vehicle car drivemeans controlled by a plurality of bistable devices, the combinationcomprising:

control means for providing a plurality of control signals to each ofsaid vehicle cars,

a first one of said plurality of bistable devices on each of saidvehicle cars being responsive to the provision of a first one of saidplurality of control signals for initially increasing the torque exertedby each of said vehicle cars; and

signal means, in a given vehicle car, including an electronicallycontrolled series conduction path between said given vehicle car and asecond vehicle car with a second one of said plurality of bistabledevices being included in said series conduction path and beingresponsive to a second one of said plurality of control signals being ata first predetermined step of signal level for changing the state ofsaid second one of said bistable devices for further increasing thetorque exerted by said given vehicle car, said signal means beingresponsive to said second one of said plurality of control signals beingat a second predetermined level for changing the condition of saidseries conduction path from open to closed for transmitting said secondone of said plurality of control signals from said given vehicle car tosaid second vehicle car for increasing the torque exerted by said secondvehicle car.

3. The combination claimed in claim 2, wherein at least one of theremaining bistable devices in each vehicle car changes state forincreasing torque in response to a third one of said control signalsbeing provided and said second one of said bistable devices havingpreviously changed state for increasing torque.

4. In a control system for selectively increasing and decreasing thetorque exerted by each of a plurality of vehicle cars operative as avehicle train, each such vehicle car having individual vehicle car drivemeans controlled by a plurality of bistable devices, the combinationcomprising:

control means for providing a plurality of control signals to each ofsaid vehicle cars;

a first one of said plurality of bistable devices on each of saidvehicle cars being responsive to the provision of a first one of saidplurality of control signals for changing from a first bistable state toa second bistable state for initially increasing the torque exerted byeach of the respective vehicle cars; and

signal means, in a given vehicle car including an electronicallycontrolled series conduction path between said given vehicle car and asecond vehicle car, with a second one of said plurality of bistabledevices in said given vehicle car being included in said seriesconduction path and being responsive to a second one of said pluralityof control signals for changing from a first bistable state to a secondbistable state for further increasing the torque exerted by said givenvehicle car, said signal means in said given vehicle car beingresponsive to said second one of said plurality of control signals beingat a predetermined step of signal level for changing the condition ofsaid series condduction path from open to closed for applying saidsecond one of said plurality of control signals to said second vehiclecar.

5. The combination claimed in claim 4 including a third one of saidplurality of bistable devices on said given vehicle car being responsiveto either one of (a) a third one of said plurality of control signals or(b) said first one of said plurality of control signals and said secondone of said plurality bistable devices being in the second bistablestate, for changing from a first bistable state to a second bistablestate for further increasing the torque exerted by said given vehiclecar.

6. The combination claimed in claim 5 including a fourth one of saidplurality of bistable devices on said given vehicle car being responsiveto said third one of said plurality of control signals and said secondone of said plurality of bistable devices being in the second bistablestate, for changing from a first bistable state to a second bistablestate for further increasing the torque exerted by said given vehiclecar.

7. The combination claimed in claim 6 including a fourth one of saidplurality of control signals, which functions as a holding signal and isapplied to said third and fourth ones of said plurality of bistabledevices when said third and fourth ones of said plurality of bistabledevices are respectively in the second bistable state for maintainingsaid bistable devices in the second bistable state.

8. The combination claimed in claim 4 including a third one of saidplurality of bistable devices on said given vehicle car being responsiveto a third one of said plurality of control signals for changing from afirst bistable state to a second bistable state for further increasingthe torque exerted by said given vehicle car.

9. The combination claimed in claim 8 including a fourth one of saidplurality of bistable devices on said given vehicle car being responsiveto a fourth one of said plurality of control signals for changing from afirst bistable state to a second bistable state for further increasingthe torque exerted by said given vehicle car, and including means formaintaining said fourth bistable device in said second bistable state inresponse to said first one of said plurality of control signals andeither one of said second or third ones of said plurality of bistabledevices, being in the second bistable state.

10. The combination claimed in claim 9 including a fifth one of saidplurality of bistable devices on said given vehicle car being responsiveto (a) said fourth one of said plurality of control signals and (b) saidsecond and third ones of said plurality of bistable devices beingconcurrently in the second bistable state, for changing from a firstbistable state to a second bistable state for further increasing thetorque exerted by said given vehicle car.

11. The combination claimed in claim 10 including means for maintainingsaid fifth one of said plurality of bistable devices in said secondbistable state in response to either one of said second and third onesof said plurality of bistable devices being in the second bistablestate.

* i i t

1. In a control system for selectively increasing and decreasing thetorque exerted by each of plurality of vehicle cars operative as avehicle train, each such vehicle car having individual vehicle car drivemeans controlled by a plurality of bistable devices, the combinationcomprising: control means for providing at least one vehicle controlsignal; and means, in a given one of said vehicle cars, including anelectronically controlled series conduction path between said given oneof said vehicle cars and a second vehicle car with a given one of saidplurality of bistable devices being included in said series conductionpath and being responsive to said one vehicle control signal being at afirst predetermined level for changing the state of said given one ofsaid plurality of bistable devices for increasing the torque exerted bysaid one vehicle car, said means being responsive to said one vehiclecontrol signal being at a second predetermined level for changing thecondition of said series conduction path from open to closed fortransmitting said one vehicle control signal from said one vehicle carto said second vehicle car for increasing the torque exerted by saidsecond vehicle car.
 2. In a control system for selectively increasingand decreasing the torque exerted by each of a plurality of vehicle carsoperative as a vehicle train, each such vehicle car having individualvehicle car drive means controlled by a plurality of bistable devices,the combination comprising: control means for providing a plurality ofcontrol signals to each of said vehicle cars, a first one of saidplurality of bistable devices on each of said vehicle cars beingresponsive to the provision of a first one of said plurality of controlsignals for initially increasing the torque exerted by each of saidvehicle cars; and signal means, in a given vehicle car, including anelectronically controlled series conduction path between said givenvehicle car and a second vehicle car with a second one of said pluralityof bistable devices being included in said series conduction path andbeing responsive to a second one of said plurality of control signalsbeing at a first predetermined step of signal level for changing thestate of said second one of said bistable devices for further increasingthe torque exerted by said given vehicle car, said signal means beingresponsive to said second one of said plurality of control signals beingat a second predetermined level for changing the condition of saidseries conduction path from open to closed for transmitting said secondone of said plurality of control signals from said given vehicle car tosaid second vehicle car for increasing the torque exerted by said secondvehicle car.
 3. The combination claimed in claim 2, wherein at least oneof the remaining bistable devices in each vehicle car changes state forincreasing torque in response to a third one of said control signalsbeing provided and said second one of said bistable devices havingpreviously changed state for increasing torque.
 4. In a control systemfor selectively increasing and decreasing the torque exerted by each ofa plurality of vehicle cars operative as a vehicle train, each suchvehicle car having individual vehicle car drive means controlled by aplurality of bistable devices, the combination comprising: control meansfor providing a plurality of control signals to each of said vehiclecars; a first one of said plurality of bistable devices on each of saidvehicle cars being responsive to the provision of a first one of saidplurality of control signals for changing from a first bistable state toa second bistable state for initially increasing the torque exerted byeach of the respective vehicle cars; and signal means, in a givenvehicle car including an electronically controlled series conductionpath between said given vehicle car and a second vehicle car, with asecond one of said plurality of bistable devices in said given vehiclecar being included in said series conduction path and being responsiveto a second one of said plurality of control signals for changing from afirst bistable state to a second bistable state for further increasingthe torque exerted by said given vehicle car, said signal means in saidgiven vehicle car being responsive to said second one of said pluralityof control signals being at a predetermined step of signal level forchanging the condition of said series condduction path from open toclosed for applying said second one of said plurality of control signalsto said second vehicle car.
 5. The combination claimed in claim 4including a third one of said plurality of bistable devices on saidgiven vehicle car being responsive to either one of (a) a third one ofsaid plurality of control signals or (b) said first one of saidplurality of control signals and said second one of said pluralitybistable devices being in the second bistable state, for changing from afirst bistable state to a second bistable state for further increasingthe torque exerted by said given vehicle car.
 6. The combination claimedin claim 5 including a fourth one of said plurality of bistable deviceson said given vehicle car being responsive to said third one of saidplurality of control signals and said second one of said plurality ofbistable devices being in the second bistable state, for changing from afirst bistable state to a second bistable state for further increasingthe torque exerted by said given vehicle car.
 7. The combination claimedin claim 6 including a fourth one of said plurality of control signals,which functions as a holding signal and is applied to said third andfourth ones of said plurality of bistable devices when said third andfourth ones of said plurality of bistable devices are respectively inthe second bisTable state for maintaining said bistable devices in thesecond bistable state.
 8. The combination claimed in claim 4 including athird one of said plurality of bistable devices on said given vehiclecar being responsive to a third one of said plurality of control signalsfor changing from a first bistable state to a second bistable state forfurther increasing the torque exerted by said given vehicle car.
 9. Thecombination claimed in claim 8 including a fourth one of said pluralityof bistable devices on said given vehicle car being responsive to afourth one of said plurality of control signals for changing from afirst bistable state to a second bistable state for further increasingthe torque exerted by said given vehicle car, and including means formaintaining said fourth bistable device in said second bistable state inresponse to said first one of said plurality of control signals andeither one of said second or third ones of said plurality of bistabledevices, being in the second bistable state.
 10. The combination claimedin claim 9 including a fifth one of said plurality of bistable deviceson said given vehicle car being responsive to (a) said fourth one ofsaid plurality of control signals and (b) said second and third ones ofsaid plurality of bistable devices being concurrently in the secondbistable state, for changing from a first bistable state to a secondbistable state for further increasing the torque exerted by said givenvehicle car.
 11. The combination claimed in claim 10 including means formaintaining said fifth one of said plurality of bistable devices in saidsecond bistable state in response to either one of said second and thirdones of said plurality of bistable devices being in the second bistablestate.